Hi, I'm getting this problem as well. I'm running vB 3.6.8 and the latest ibProArcade v2.6.3+, and I have holdsession.php in my forum's root directory. I'm not using vbadvanced or another Portals.
Testing with Pacman:
With $DEBUG set to 2, I get the following error message when trying to save a score:
This score was not submitted from the game. Your score will not be saved.
Error #023 - no session
It'll auto logout the user and go to the page: /forums/index.php?act=Arcade&do=newscore
even though this test was performed well within the cookie expiry time.
I noticed that this problem only seems to occur when the score it's trying to save exceeds 10,000. If it's below 10,000 then it can save without any errors, at least in Pacman.
However, if the user had logged in to vB with "Remember me" checked, then there doesn't seem to be any problem saving a score higher than 10,000!
This isn't making any sense to me, but I hope it is for you MrZeropage, or for anyone who is familar with this addon script. Appreciate your advise.